Afterwards I did some testing of core temperatures using iLO and Open Hardware Monitor. When heavily loaded with Prime95 I found it alarming that the core temperatures would rise steadily to about 85 degrees C in Open Hardware Monitor. The system fan speeds (the fan had been set to Optimal Cooling in BIOS) would also rise steadily from 6% to 21% where the temperature rise was arrested with iLO CPU temps of 60C.

Figure 3 — Open Hardware Monitor showing individual Core Temperatures of CPU Cores as well as other useful data.

Sandpaper, wet/dry type, starting at 400 grit, 800, 1000, 1500, & 2000. If you want you could add 600, 1200, & 2500 to that mix. Start with 400 and when Face is Flat THEN work your way up to achieve a mirror finish.

Figure 6 — Preparing to Clean the Heat Sink & CPU then test the Face of the Heat Sink for Flatness

In this Video (Video 3: Clean Heat Sink & CPU: HP ProLiant Gen8 MicroServer) I clean thermal material off of the Heat Sink & CPU, then I confirmed that the face of the CPU Heat Sink was not flat:

Figure 7 — By lifting the Heat Sink up and looking along the face of the Heat Sink with the metal Straight Edge across the Heat Sink and the overhead lights behind the Straight Edge and Heat Sink I confirmed that the Heat Sink face was NOT flat. See Figure 8 & Video 3.

Figure 8 — By lifting the Heat Sink up and looking along the face of the Heat Sink with the metal Straight Edge across the Heat Sink and the overhead lights behind the Straight Edge and Heat Sink I confirmed that the Heat Sink face was NOT flat. See Figure 7 & Video 3.

Figure 9 — Preparing to Lap the Heat Sink using wet/dry sandpaper

Figure 10 — 12″ X 10″ piece of glass to be used as base for the Sandpaper during lapping

Figure 11 — Mirror finish on Heat Sink after Lapping

Update 2/13/2014

Al_Borges, a member of our HSS forums, who I had the good fortune to meet at the #BestEverMeetup #2013MeetUp shared with me some of his knowledge as a Metallurgist in the Aluminum Industry about lapping AL – which he does regularly to view AL samples metallographically.

“Your basic technique was fine – however, you would have had much better and faster results if you had started with 80 or 120 grit – followed up with 220 then lastly 400. Lubricating it with water will also help.

The aluminum oxide you are sanding off is as hard as the grit. Sanding with too fine a grit will let the particles ball up between the work piece and the tool and you won’t get any metal removal. The coarser grits will cut into the surface.”

Many Thanks to Al_Borges and I hope this information will help others in the future should they find the need to lap their Heat Sink to get a flat surface on it.

So bottom line, If I was to do it over again, I would start with the 80 or 120 grit wet/dry sandpaper and after getting the heat sink face flat I would move up to the 220 then the 400 then I could have stopped.

Figure 16 — 7 Day (168 hours) break-in run with Fans set in BIOS to “Increased Cooling” resulting in fan speeds from 36% to 41% during that period.

Additional testing of temperatures under heavy load will be discussed in a subsequent report.

Conclusion

I removed and tested the CPU Heat Sink from my Gen8 MicroServer and found that it was not flat. I then lapped the Heat Sink until it was flat and reassembled my Gen8 MicroServer. I’ve allowed it run at different power levels during the 200 hour break-in period for Arctic Silver 5, after which, I will do some additional temperature testing and response to heavy loads.